The invention discloses a locking and unlocking method of a hydraulic torque converter. The method comprises the following steps of: obtaining a turbine rotation speed and an engine rotation speed under the current throttle state; calculating to obtain rotation speed ratio, wherein the rotation speed ratio is a specific value of the turbine rotation speed to the engine rotation speed; if the rotation speed ratio is in a preset rotation speed ratio range, keeping the current working state of the hydraulic torque converter; when the rotation speed ratio is judged to be higher than a locking rotation speed ratio in the preset rotation speed ratio range, locking the hydraulic torque converter; when the rotation speed ratio is judged to be lower than the unlocking rotation speed ratio in the preset rotation speed ratio range, unlocking the hydraulic torque converter. According to the method, system and the construction machine provided by the invention, the working state of the current construction machine is determined according to the specific value of the turbine rotation speed to the engine rotation speed, thereby realizing locking and unlocking of the hydraulic torque converter; and the problems that the transmission efficiency is low and the oil consumption and the pollution are increased caused by the fact that the hydraulic torque converter works under the condition that the working efficiency of the construction machine is lower can be solved.